Temperature field and residual stress distribution for laser metal deposition

Abstract

Laser metal deposition (LMD) process has been widely used in many industrial applications such as automotive, defense, aerospace, and so on. Modeling has to address physical phenomena like laser-powder interaction, heat transfer, fusion, solidification, and track formation. LMD induces a complex thermal stress field that results in residual stress distributions. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stresses can cause unpredicted in-service failures. Therefore, the prediction of its distribution in the deposited structure as a function of the process strategy is essential to improve the process and the part quality. LMD represents mathematically a free boundary value problem. This means that the track geometry is part of the solution. The authors developed a three-dimensional time-dependent finite element model for LMD with coaxial powder feeding supply. The model encompasses the powder stream, its interaction with the laser radiation, and the melt pool computation. The model was validated by a comparison of the experimental and computed shapes of the melt pool surfaces concerning cross section, longitudinal section and high-speed photographs [Pirch et al., in Proceedings of the ICALEO Conference, 16–20 October 2016]. In this paper, the model was applied to overlapping tracks for single and multilayer processing for different process strategies. The simulation allows us to analyze the time- and space-resolved evolution of temperature and stresses. The influence of the powder feed rate on the residual stresses is investigated.